In order to increase the energy content of energy carriers that are gaseous under normal conditions, these are either compressed for transport and storage purposes and stored in pressurized tanks, or cooled to a low temperature and thereby liquefied, at least in part, as a cryogenic fluid, and stored in temperature-insulated containers. Liquefied natural gas (LNG) or liquefied hydrogen, for example, are stored as cryogenic fluids having great energy density, for powering vehicles, and are subsequently utilized to power essentially conventional internal combustion engines or fuel cells of the vehicles.
Aside from the low temperatures, in the case of LNG up to minus 161° C., for example, the container must withstand the elevated pressure of the cryogenic fluid, in the case of LNG up to 16 bar, and therefore has a circular cylindrical cross-section. For insulation, the container is double-walled, where the insulation gap that lies between the two walls is generally evacuated and/or lined with special insulation films/foils. LNG is easier to handle than liquid hydrogen, for example, and more environmentally friendly and cost-advantageous than conventional fuel, such as gasoline or diesel fuel, and therefore of particular interest specifically for utility vehicles having high fuel consumption or a high degree of utilization, for example trucks. On the other hand, neither LNG nor liquid hydrogen is available in a broad distribution network, and because of the low temperature and the high pressures, they are more difficult to store than conventional fuel.
In principle, LNG can be used both in gasoline engines and in diesel engines; when used in engines that work according to the diesel principle, additional diesel fuel is required for ignition. In order to increase the vehicle range and to allow operation with LNG, conventional fuel is frequently carried along in addition, in vehicles equipped for this purpose. This conventional fuel, just like other operating materials, for example AdBlue®, hydraulic oil, etc., is stored in separate tanks for operating materials, and this requires additional construction space.